Panoramic radiographs may be obtained by directing an X-ray beam through an object to be X-rayed to a moving X-ray film while rotating the X-ray source and film about the object. In obtaining panoramic radiographs of the dental arch area however, compensation must be made for the fact that the curvature of the desired area of focus is generally not a true circle or ellipse.
Various cam mechanisms have been provided for varying the rate of film travel relative to the rate of travel of the X-ray source about the patient's head in order that the radiological projections occupy a distance on the film equal to the linear distance of a curved structure being X-rayed, such as a typical dental arch. These cam mechanisms, however, have usually required separate motors, i.e., one motor for rotating the tubehead-camera assembly about the patient's head, and the other motor for driving the cam mechanism which controls the rate of travel of the film. Such motors oftentimes lacked synchronization resulting in radiographs of doubtful value, or the entire tubehead-camera-film drive assembly required constant synchronous adjustment.
The present invention completely obviates the need for separate motors by providing a reliable film drive mechanism which operates in response to rotation of the tubehead-camera assembly which requires but a single motor for rotation.